最新刊期
卷 27 ， 期 1 ， 2006
- 摘要：Thin film electroluminescence, TFEL, is one of the most important material of flat panel display. Researching work on TFEL is sustained until now. We have started stable EL from ZnS:Mn,Cu thin film, at first, and doped with rare earth ions into thin film, realized various color DCEL and studied excitation mechanism, energy distribution of hot electrons, impact section of rare earth ion and the position of rare earth ion in crystal lattice. At first, in our country we have worked out computer terminal display device of TFEL and made it in large area (640×480 lines). In order to realize color TFEL display, we have fabricated different color TFEL doped with different rare earth ions, studied concentration quenching of rare earth ions in TFEL and their mechanism, guided to fabricate material and increase EL brightness. In process of realizing color display of TFEL, the first task is increasing brightness of blue TFEL and searching new blue TFEL material. We improved AnS:TmF3 to CaS:TmF3 which brightness was greatly increased, fabricated SrS:Ce blue TFEL with high brightness over 1000 cd/m2, found nano-meter Si and non-crystal Si/SiO2 superlattice structure of blue EL, obtained white EL in ZnS:Mn/SrS:Ce and SrS:Ho3with three basic color line spectrum emission with high brightness over 1000cd/m2.关键词：electroluminescence;thin film;flat panel display129|192|2更新时间：2020-08-11
- 摘要：A charged particle moving along the direction of the low crystal face index can penetrates through the crystal as easily as it does through a channel. This phenomenon is so-called channeling effect. The classical physics points out that an accelerated charged particle radiates energy spontaneously when moving in an electromagnetic field. The analogous situation occurs in crystal channel. When a charged particle moves in an accelerated way through a lattice field, the radiation energy can be produced. The behaviours of the charged particles moved in a crystal channel are controlled by the interaction potential between a charged particles and the crystal. Usual interaction potential is Lindhad potential, Moliere potential and Sine-squared potential. The channeling radiation is described analytically by using the sine-squared potential. The bend of the crystal is equivalent to constant moment. Thus in a framework of the classical mechanics the motion equation of a particles in a bent crystal is reduced to pendulum equation with a constant moment by using the sine-squared potential.The phase planar properties of the system are analyzed by the numerical method.In the small amplitude approximation the motion equation of a particles is reduced to the equation for the hard spring-oscillator.The solution of the equation and the period of the particle motion are expressed exactly by means of Jacobian elliptic function and 1st kind elliptic integral.The properties of the radiation spectrum is discussed.It pointed out it is possible to take channeling radiation as a new γ-Laser.As example, maximum radiation frequence,deflective angle ψ of a positron in the carbon crystal are calculated.The result is coincident basically with other work.关键词：bent crystal;channeling radiation;nonlinearity;sine-squared potential109|112|0更新时间：2020-08-11
- 摘要：In the past dozens of years, with the development of magneto-optical technology, the properties of the polaron in a magnetic field have been widely studied both experimentally and theoretically. However, the properties of magnetopolaron have not been investigated by Huybrechts method so far. The excitation energy of the strong coupling surface polaron have been calculated using Huybrechts method by the present authors and co-workers. The properties of the surface magnetopolaron in polar crystals were studied. The ground state vibration frequency and the effective Hamiltonian of surface magnetopolaron were derived by using the linear combination operator and the unitary transformation method. Two limiting cases of the coordinate z for the electron-SO phonon and electron-LO phonon system are discussed. Numerical calculations, for the RbCl crystal as an example,are performed. We find that due to the existence of the surface optical (SO) phonons, the electrons move more close to the surface,the interactions between the electrons and the SO phonons become more strong. When the electron infinitely close to the surface, the contribution of the LO phonon can be neglected. On the other hand, the contribution of the bulk LO phonon will increase with the increase of the distance between electron and the surface. At this moment, the contribution of the bulk LO phonon is much greater than SO phonon's, and then we can omit the SO phonon. The results show that the vibration frequency and the parallel effective Hamiltonian of surface magnetopolaron will be increased with increasing magnetic field. The reason is that with the increase of magnetic field the location of the magnetopolaron will be enhanced.关键词：surface magnetopolaron;strong coupling;effective Hamiltonian118|96|0更新时间：2020-08-11
- 摘要：During the last two decades, the development of fabrication technique have made available structures whose dimensions are much smaller than the characteristic length such as the mean free path and phase coherence length of an electron. These structures are referred to as mesoscopic system. The physical properties of the mesoscopic system are strongly affected by quantum interference effects. So it is an important question for discussing the transport properties of the electron in mesoscopic structures and it is physics gist to construct quantum devices. Up to now there have been lots of investigations about the mesoscopic system by using varieties theories and experimental methods. But the transport properties of the electron in one-dimensional double stub mesoscopic structures have not been studied. We discuss the transmission properties of electron in double stub mesoscopic structures with quantum waveguide theory. For the sake of simplicity we consider a coherent, dissipationless, quasi-one-dimensional system, and neglect scattering at the junction. We found that the transmission coefficient of electron in one-dimensional double stub mesoscopic structures oscillates with changing the length of the stub and the length of the ring. The transmission coefficient of the electron can be modulated up to 100% by modulating length of the stub and the length of the ring and it is very interesting to notice that the transmission coefficient of the electron modulated by two stubs is better than that modulated by one stub. The theory study is maybe valuable for the study of quantum devices.关键词：quantum waveguide theory;mesoscopic structures;electron transport130|114|0更新时间：2020-08-11
- 摘要：There are very few direct measurement techniques that can be used to establish the movement of carriers in powders and polycrystals.The microwave absorption dielectric spectrum detection technique is suitable for investigating dynamic processes undergone by photocarriers of semiconducting nanomaterials, powder luminescent materials, micropowder,nanocrystal materials and multicrystal membrane materials.Investigation of the kinetic decay process for free photoelectrons and shallow trapped electrons is helpful in achieving and understanding of the kinetic mechanism of luminescence and the energy level structure for luminescent material or other semiconducting crystal materials;also, it can provide a scientific basis for the improvement of the luminescence efficiency of semiconducting materials. The decay process of photoelectrons of ZnS powder materials after excitation with short pulse laser has been measured by microwave absorption method. The materials were prepared under different flux and protective gas. The thermoluminescence spectra of the materials has also been investigated. Sample A was sintered at 1 150℃ with excessive SrCl as flux. The thermoluminescence spectra showed that there were shallow-electron traps and the density of that was low. The decay processes of photoelectrons included two exponential decay processes and the lifetime of the fast process and the slow process were 45 ns and 312 ns respectively. Sample C was prepared with a small quantity of NaCl as flux. The thermoluminescence spectra of it showed that there are high density of shallow-electron traps and deep-electron traps in the materials. Its lifetime is 1 615 ns. The lifetime of Sample B which was sintered under NH4Br protective gas is 1 413 ns and only shallow-electron traps was formed. It was proved that the lifetime of photoelectrons has close relation with the density of shallow-electron traps. The higher the density was, the longer the lifetime. But deep-electron traps have little effect on the instant process of photoelectrons.关键词：ZnS;microwave absorption;thermoluminescence;photoelectron129|131|0更新时间：2020-08-11
- 摘要：Er3+ /Yb3+ codoped tungsten-tellurite (WT) glasses, TeO2-WO3-RmOn (RmOn =PbO, BaO, La2O3, Bi2O3), were prepared and investigated. WO3 has been introduced in the tellurite glasses due to the following two reasons: The first one is to increase the phonon energy and the!multi-phonon relaxation rate of the Er3+ :4I11/2→4I13/2 transition, which benefits the population inversion between the 4I13/2 and 4I15/2 level of Er3+.The second is to enhance the thermal stability against crystallization. The structural studies were done through FT-IR spectral analysis and revealed that these glasses contain TeO4, TeO3, WO4 and WO6 units as the local structures. The asymmetry of Er3+ sites results in inhomogeneous broadening of spectra and large emission cross-section at 1.5 μm band. The fluorescence full width at half maximum FWHM=77 nm, and the peak of the emission cross-section σpeak =1.03×10-20cm2, are manifested in 70TeO2-20WO3-10Bi2O3 glass. The gain bandwidth properties, FWHM×σepeak,of Er3+ in WT glasses have advantages over those of bismuthate, phosphate, tellurite and silicate glasses, indicating the WT glasses are promising host materials for 1.5 μm broadband amplification.关键词：spectral properties;Er3+/Yb3+ codoped;tungsten-tellurite glass;thermal stability127|338|0更新时间：2020-08-11
- 摘要：As novel functional materials, long afterglow phosphors are drawing more and more attention in recent years because of a constantly growing market for their applications in traffic signs, emergency signage, watches and clocks, textile printing, among others. Amid the newly developed long afterglow materials which have already found commercial use, blue-emitting Sr2MgSi2O7:Eu2+,Dy3+ is of special interest because of its excellent persistent luminescence combined with an easy processability. In this paper, the luminescent properties and long afterglow of Sr2MgSi2O7:Eu2+,Dy3+ were investigated using synchrotron radiation and VUV laser (157.6 nm) as excitation sources.The emission spectra of Sr2MgSi2O7:Eu2+,Dy3+ under 170 nm synchrotron radiation excitation consists of a 477 nm broad band corresponding to 5d-4f transitions of the Eu2+ ions and two group of line spectra corresponding to 4F 9/2→6H15/2 transitions (478, 483 and 493 nm) and 4F9/2→6H13/2transitions (574, 576, 579, 581 and 585 nm) of Dy3+,respectively. The excitation spectra of 477 nm emission is dominated by an excitation band at wavelengths longer than 220 nm, which shows a complicated structure, comprising at least three sub-bands (around 250, 280 and 310nm), corresponding to the transition from 8S7/2 to the higher crystal field components of 4f65d1 states of Eu2+.The relatively weaker 170 nm excitation band was ascribed to spin allowed f-d transition of Dy3+. At different temperature, the long afterglow emission after irradiation of 170 nm synchrotron radiation was measured 30 seconds after closing the beam-shutter. As in the case of Eu2+ and Dy3+ codoped MAl2O4 (M=Ca and Sr), the long afterglow emission of Sr2MgSi2O7:Eu2+,Dy3+ is due to the 5d-4f transitions of the Eu2+ ions. The laser excited emission spectra exhibit some new features comparing to the synchrotron radiation excited emission spectra. The most obvious new features are three groups of sharp emission lines centred around 590, 614 and 626 nm, which are known to be the red emissions of trivalent europium corresponding to intraconfigurational 4f-4f transitions. The strong emission from Eu3+ indicates an efficient photon-induced process, promoting Eu2+ to Eu3+,caused by the much higher excitation density of laser source.The high efficiency of Eu2+-Eu3+ conversion by laser perhaps implies a high possibility of Eu2+ ions acting as hole traps("Eu2++h"), which is neglected by now in the study of Eu2+ doped long afterglow phosphors, but may play an important role in the process of the persistent luminescence. At room temperature, the holes are thermally released continuously from these hole traps at Eu site, preparing the Eu2+ ions to accept the energy released by the electron-hole recombination (perhaps via cross relaxation), and finally yielding the long afterglow emission from Eu2+ ions.关键词：long afterglow phosphor;rare earth;Sr2MgSi2O7：Eu2+;Dy3+;luminescence117|137|3更新时间：2020-08-11
- 摘要：Er3+-doped and Er3+/Yb3+-codoped materials have played an important role in the development of broadband erbium-doped fiber amplifiers (EDFA) at the third communication window for their potential laser applications. Therefore, the choice of host material is very important in the development of more efficient op-tical amplifiers based on Er3+-doped glasses.The new Er3+ /Yb3+-codoped 70TeO2-5Li2O-10B2O3-15GeO2 glass was prepared by the technique of high-temperature melting. The thermal stability, absorption spectra, fluorescence spectra and FT-IR spectra were measured and investigated. The effect of OH- on the spectro-scopic properties of glass sample was discussed. The Judd-Ofelt theory analysis on the absorption spectra was performed and compared with other glass hosts. The oscillator strength, spontaneous emission probability, radiative lifetime and emission branching ratio of several Er3+ transitions were calculated according to the obtained Judd-Ofelt parameters. It was found that this studied glass has good thermal stability and it is a perfect candidate material for fiber drawing. The Judd-Ofelt parameters deriving from the absorption spectra were acquired as follows: Ω2=5.65×10-20 cm2, Ω4=1.21×10-20 cm2, Ω6=0.95×10-20 cm2. The broad FWHM(77 nm) was obtained from the fluorescence spectra and the large stimulated emission cross-section σepeak (8.7×10-21 cm2) was calculated by the McCumber theory. The product of FWHM× σepeak is larger than those of other glass hosts, which indicating that this studied glass may be a potentially useful candidate material host for broadband optical amplifier. In addition, the fluorescent intensity and lifetime of the 4I13/2 level of Er3+ ions will decrease with the existence of OH-content. The lifetime of the 4I13/2 level of Er3+ ions increase from 1.7 ms to 2.31 ms after removing water during the melting process.关键词：germanotellurite glass;thermal stability;spectroscopic properties;Judd-Ofelt theory;OH~-114|60|0更新时间：2020-08-11
- 摘要：There has been an intense interest in the investigation of ultra-fine and nanocrystalline oxide upconversion materials these years for potential applications in upconversion phosphors, detectors for infrared radiation, fluorescent labels for sensitive detection of biomolecules and two-photon confocal-microscope imaging. Numerous host materials, such as Y2O3, Gd2O3, ZrO2, TiO2 and BaTiO3, have been investigated as host material for upconversion phosphors due to their low phonon-vibration frequencies. Er3+ doped materials are well suitable for upconversion because the metastable levels 4I9/2 and 4I11/2 of Er3+ can be conveniently popu-lated by low-cost high-power 800 nm and 980 nm laser diodes, respectively. The sensitization of Er3+ doped materials by Yb3+ ions is a well-known method for increasing the optical pump efficiency because of the high absorption cross section of Yb3+ ions around 980 nm and the efficient energy transfer from Yb3+ to Er3+ ions. Strontium titanate (SrTiO3) is a well-known material because of its good properties, such as its high dielectric constant, high charge storage capacity, good insulating property, its chemical and physical stability and its excellent optical transparency in the visible range. In addition, similar to BaTiO3, its phonon-vibration frequency is quite low, which makes it suitable for host material as upconversion phosphors. But to the best of our knowledge, there is no reports on upconversion of Er3+ doped, Er3+/Yb3+-codoped SrTiO3 powders. Er3+-doped and Er3+ /Yb3+-codoped SrTiO3 ultra-fine powders have been prepared in a molten NaCl flux. The structure properties of the samples were examined by X-ray diffraction (XRD);Fourier transform infrared spectroscopy (FT-IR) and field emission scan electron microscopy (FE-SEM). FT-IR spectra showed that SrTiO3 powders may have higher upconversion luminescence efficiency because of its low phonon-vibration frequency. The intense green and red emissions around 528, 550 and 663 nm corresponding to the 2H11/2→4I15/2,4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ ions were observed under excitation by 980 nm. Laser power dependence and rare earths ions concentration dependence of the upconverted emissions were investigated to understand the upconversion mechanisms. Excited state absorption and energy transfer process were discussed as the possible mechanisms for the visible emissions.关键词：upconversion luminescence;SrTiO3;energy transfer process;excited state absorption104|125|4更新时间：2020-08-11
- 摘要：ZnO hexagonal sub-microrods have been synthesized onto glass substrates through aqueous growth method by using the thermal decomposition of an aqueous solution of equimolar zinc nitrate(Zn(NO3)2·4H2O) or zinc acetate(Zn(CH3COO)2·2H2O))with methenamine ((CH2)6N4) by controlling the experimental conditions. XRD patterns, SEM images have been measured, which reveals the shape of the most of the ZnO sub-microrods are hexagonal-rod with two flat faces on the two ends, but some are pair rods symmetrically grown from a center to both sides and some form radial clusters from one center. The length of the rods is from 5 μm to 8 μm, the diameter from 300 nm to 700 nm and the ratio of the length to the diameter is more than 10:1. When the growth time reaches 48 h, we found that the microrods turned into hollow microtubes with the tube-thickness in the tenth of diameter. The growth mechanism is discussed by using the growth model of cathodion ligand tetrahedron. Zn-(NO3)2 dissolves and forms growth units of tetrahedron Zn-(OH)4 under the reaction of the surface activator (CH2)6N4. Then the incorporation of growth units leads to the formation of the ZnO crystal lattice at the interface through a dehydration reaction (OH-+OH-H2O+O2-). The fastest of the growth speed along 0001-direction leads to the formation of the ZnO microrods. The reason of forming hollow microtubes is the face of (0001) and 0001 of ZnO rods as eroded by chemical dissolution because of its metastable state. The excitation spectra of ZnO sub-microrods show that except the intrinsic inter-band excitation shorter than 370 nm, there is a strong exciton excitation peak located at around 377385 nm at room temperature. The photoluminescent spectra show that there is a wide orange-red emission peaking at about 630 nm and FWHM 250 nm with the excitation wavelength 310 nm. When the excitation is a strong 325 nm He-Cd laser, the same sample will emit a strong excition emission peaking at about 385 nm, with FWHM 16 nm and a green emission peaking at about 552 nm with FWHM 120 nm. Compared with the calculated data of these intrinsic defects with the theory of FP-LMTO, the green, orange-red and red emission peaks can be attributed to the transition of oxygen vacancies to the valence band. The studies on PL of ZnO sub-microrods after annealing showed that the excitation peak at about 384 nm disappeared, and the orange-red defect emission (peak at 630 nm) shows red shift (peak at 710 nm), and the emission intensity increases. The excitation spectra of samples after annealing showed an enhanced exciton peak at 377 nm. It indicates that after annealing, the energy transfer from the excition to the defect center occurred.99|74|7更新时间：2020-08-11
- 摘要：N-doped zinc oxide (ZnO) thin films grown on c-face sapphire (c-Al2O3) substrate by plasma-assisted molecular beam epitaxy (P-MBE) in Zn-rich condition were reported. NO gas activated by a radio frequency source was used as both oxygen and nitrogen sources. The crystalline structure, chemical composition and electrical properties were investigated by X-ray diffraction (XRD) spectra, X-ray photoemission spectra (XPS) and temperature-dependent Hall effect measurement. In XRD spectra, the full width at half maximal (FWHM) of (0002) diffraction peak for N-doped ZnO was broader than that of undoped sample due to the incorporation of nitrogen atoms in the N-doped ZnO film. At the same time, X-ray photoelectron spectra (XPS) showed the atomic fractions for N, Zn and O are 1.1%, 53.7% and 45.2%, respectively. XPS results proved nitrogen atoms had occupied the oxygen lattice and acted as acceptors. It also proved that ZnO was grown in a Zn-rich condition in the experiment. However, the Hall effect measurement (at room temperature) showed the sample was still n-type conduction with a higher carrier concentration (2.15×1020 cm-3). This concentration was much higher than that of undoped sample (1018 cm-3). In order to further investigate the electrical property of ZnO, the sample was annealed in O2 ambient at 500℃ for 30 min. The temperature dependent of Hall effect measurements showed different behaviors between the as-grown and the annealed samples. Before annealing, the as-grown sample showed metal conduction behavior, while it showed normal semiconductor conduction behavior after annealing. According to theory analysis and calculation, it was believed after compensating the limited acceptor(nitrogen atoms occupied the oxygen lattice),the behavior for residual ZnO atoms is similar to heavy-doped conduction in ZnO sample and caused the ZnO sample changed from semiconductor conduction to metal condution behavior (Mott transition).关键词：ZnO thin film;X-ray photoelectron spectroscopy;Mott transition97|113|1更新时间：2020-08-11
- 摘要：High-reflectance ohmic contacts to p-GaN are the key for Flip-chip ultra-violet light emitting diode (UV-LED) to improve the external quantum efficiency (EQE), so the kinds of metal or alloy film both ohmic contact and the reflector of light are important to choose the appropriate high-reflectance and low-resistance ohmic contact to p-type GaN. The GaN-based LED samples used were grown by Metalorganic Chemical Vapor Deposition (MOCVD). Four different metal films were deposited on the surfaces of p-GaN and annealed Ni/Au alloy. The thickness of these metal films varied from 30 nm to 840 nm. The reflectance and transmittance of the samples were mea-sured by WGS-9 system. The 2θ scans XRD and surface AFM images of the samples were also observed. As results, when the films' thickness under the 130 nm the reflectance of Ag-deposited samples increased with the increasing thickness and the transmittance decreased at wavelength of 400 nm. The reason of the increasing of reflectance is the reduction of the light transmitted through the films. When the films' thickness over 130 nm, the reflectance of Ag-deposited samples decreasing. From the results of XRD and AFM, the metal film formed multi-layers film and the roughness Ra and Rq increased with the increasing thickness. It is suggested that the diffusion of the multi-layers films is the main reason of reduction of reflectance with the films thickness increasing. Other metal films show the same characteristics as the Ag-deposited films. From the result of reflectance, Al and Ag are the suitable candidates for the reflector, but it is reported that the single Al or Ag films don't make good ohmic contacts on p-GaN. So a thin annealed Ni/Au is adopted to interspersed between the Al or Ag reflector and the p-GaN in order to provide efficient hole injection into the device. From the results of reflectance and I-V curves of Ni/Au/Ag and Ni/Au/Al, the I-V characteristics of Ni/Au/Ag and Ni/Au/Al contacts are similar to this of Ni/Au annealed. However the reflectance of Ni/Au/Ag and Ni/Au/Al contacts is three times higher than that of Ni/Au at wavelength of 400 nm. These results demonstrated that Ni/Au/Ag and Ni/Au/Al can be used as high-reflectance and low-resistance p-GaN ohmic contacts for flip-chip UV-LEDs关键词：violet LED;GaN;reflectance;ohmic contact118|170|0更新时间：2020-08-11
- 摘要：GaN-based light-emitting diodes provide higher performance in the short-wavelength part of the visible and ultraviolet spectrum than any other material system. However, there is still a great need for improvement of the extraction efficiency. Because many parts of emitting light of LED suffer absorption of the metal contacts and bond pads, also by active layer. So the employment of highly reflective metal ohmic contacts with a low contact resistance could substantially improve the GaN extraction efficiency of GaN-based LED, especially for vertical structure LED fabricated by laser lift-off process, which have more light output surface and high thermal conductivity than normal structure LED. The high reflectivity of omni-direction reflector is reported, that is, incorporation of Ag and Al onto the contact layers acting as a reflecting layer. Firstly, the reflectivity of the layers Ti/Ag, Al, Ni/Au/Ti/Ag and Ni/Au/Al were calculated through the theory of optical films. Then the reflectivity and contact characteristic of the GaN-based LED samples with these multi-layers on p-type GaN were measured. The result showed high omni-directional reflectors can be achieved over Ag-based films structure, and Al-based also, but the Ag-based films can provide higher reflectivity of 80%, which is better than that of Al-based film. The current-voltage curves showed low resistance on these contact layers except the Al direct on p-GaN. And the resistance of Ni/Au/Ti/Ag and Ni/Au/Al just depends on the annealed Ni/Au layers. Here the Ni/Au layers not only supply the ohmic contact but also the spreading the current. The conglomerate and oxidation of Ag film under high temperature are eliminated by introducing other Ni/Au cladding layers. Because the thickness of Ag is enough for high reflectivity so the additional layers after Ag also have no effect on the reflectivity. The good stability, low resistance and high reflectivity were obtained by two-step annealing methods. Then we applied the multi-layer Ni/Au/Ti/Ag/NiAu to vertical structure light emitting diodes (LED) by laser lift-off technology. The light output efficiency was improved significantly. The vertical structure LED with high reflective contact layer was fabricated successfully.关键词：p-GaN;ohmic contact;high reflective contact;two-type anneal method;laser lift-off;vertical structure LED129|85|3更新时间：2020-08-11
- 摘要：Cyclic voltammetry measurements for the blue-emitting conjugated PF and its derivatives were reported.Both oxidation and reduction potentials onsets were determined and thus the ionization potentials Ip and electron affinities Ea of the polymers under the same experimental condition were estimated. The oxidative potential onset of PF was at 0.97 V and the reductive potential onset at-2.58 V. In order to increase the electron-accepting ability, the bipyridine units were introduced to the polymer backbone (PP). PP3(with 50% bipyridine content) displayed greater potential change in the reductive potential (-0.37 V) compared with PF because the bipyridine in PP3 is an electron-deficient. PP3 showed a good electro-accepted ability. The Ea was increased from the 2.05 eV to 1.92 eV compared with that of PF. In the anodic scan, the onsets of oxidation of PS, PO, PC and PD was at 1.10, 1.11, 1.10 and 1.06 V which correspond to the ionization potential (Ip) values of 5.73, 5.74, 5.73 and 5.69 eV.The electron affi-nity (Ea) values of the polymers were determined to be 2.16, 2.08, 1.92 and 1.96 eV. The incorporation of the seven-membered ring moiety into the polymer backbone led to wider bandgaps. It indicates that the seven-membered ring compound was an efficient segment for tailoring the band gap of the conjugated polymer. The shift of redox potential, change of the ionization potential and electron affinity were due to the different seven-membered ring structures. The band gap of the PF derivatives was increased by introducing the seven-membered ring, especially for the meta-linkage polymers. The electrochemical energy gap agrees well with the optical energy for these copolymers.关键词：polyfluorene;cyclic voltammetry;electron affinity;ionization potential124|144|7更新时间：2020-08-11
- 摘要：The formation of intermolecular aggregation is the main reason for the phenomena that the photoluminescence (PL) efficiency of trimeric phenylenvinylene (TPV) and its derivatives, which are bright pure blue emitters, is much weaker in solid state than that in dilute solution (over 90%). In order to prevent the aggregation of TPV and achieve high-efficient emission in solid state and films, a new class of dimeric TPVs was synthesized, in which two TPVs are linked through the phenyl-phenyl bond of central phenylene ring to form a crossing dimeric structure with ~70° twisting between two TPVs planarity. The electroluminescent properties of 2,5,2',5'-tetrakis(4'-biphenylenevinyl)-biphenyl (TBVB) have been studied. According to the PL spectrum of the material, blue and white non-doped organic light-emitting devices (OLEDs) using TBVB as a blue light-emitting layer were fabricated. The structure of the blue device is ITO/NPB/TBVB/Alq3/LiF/Al, where tris(8-hydroxyquinoline) aluminum (Alq3), N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) and TBVB are used as electron-tansporting, hole-transporting and light-emitting layers, respectively. For the blue device with 30-nm-thick TBVB, the maximum luminances and efficiencies are 2154 cd/m2 and 1.62 cd/A, respectively. The structure of white devices is ITO/NPB/TBVB/rubrene/Alq3/LiF/Al, in which Alq3, NPB, TBVB and an ultrathin layer of 5,6,11,12-tetraphenylnaphthacene (rubrene), which is inserted between Alq3 and TBVB layers, are used as electron-transporting, hole-transporting, blue and yellow light-emitting layers, respectively. A fairly pure white OLED with CIE coordinates of (0.33, 0.34) at 4000 cd/m2 is realized when the thickness of TBVB is 10 nm and that of rubrene is 0.15 nm. The maximum luminance and efficiency of this device are 4025 cd/m2 and 3.2 cd/A, respectively.关键词：TBVB;blue;white;OLED;non-doped109|123|0更新时间：2020-08-11
- 摘要：The most common used structure of organic light-emitting diodes is the double layer heterojunction structure. By softening the high local electric field and partly eliminating the non-radiative recombination traps at the heterojunction interface, OLEDs with bipolar transport/emitting layer (BTEL) showed improved stability. However, the detail mechanisms of this structure are still undefined. The performance of OLEDs with uniformly mixed organic layer, which was formed by co-evaporating a hole transport material TPD, and an electron transport/emissive material Alq3 was studied. We observed that the performances of OLEDs with uniformly mixed layer were strongly dependent on the thickness of the mixed-layer, and there exists an optimized thickness of mixed layer. The devices with 5 nm(thickness) mixed layer showed improved lifetime and current efficiency, while the devices with 10 nm or 20 nm(thickness) mixed layers demonstrated similar performance compared to the heterojunction devices. The single layer devices with 100 nm totally mixed layer exhibited a very poor efficiency and stability. A primary discussion on the results was given.关键词：mixed layer;organic light-emitting diodes;efficiency;lifetime118|94|0更新时间：2020-08-11
- 摘要：We report here the quickly synthesis of peri-xanthenoxanthene using microwave carbon bath for the first time. A specific reactor is assembled to prepare the production with high yield by one step. A 100 mL glass beaker containing a mixture of 2-naphthol and cupric salt is used as reactor and covered by a watch glass. Another 250 mL glass beaker containing powder is served as a thermal bath. The reactor is placed into the bigger beaker. Thermal treatment is accomplished by dielectric loss heating of the carbon powder support using microwave irradiation. The cupric salt, reaction time and content ratio of cupric salt and 2-naphthol have been studied as reaction conditions which influence the yield of peri-xanthenoxanthene. The cupric acetate showed the higher yield than other cupric salt such as CuCl2, CuBr2, CuSO4, Cu(ClO4)2, Cu(NO3)2 and Cu(p-OTs)2. The yield of peri-xanthenoxanthene increases firstly with the increase in the content ratio of Cu(OAc)2 to 2-naphthol ranging from 1:4 to 2:1, then decreases after the content ratio over 4:1. The highest yield (86.4%) is gained at content ratio of 3:1. The 1,1'-bi-2-naphthol is the main product if the heating time less than 90 s. The main product changes to peri-xanthenoxanthene over 100 s heating time and the yield of peri-xanthenoxanthene is hardly changed at the heating time was from 150 s to 270 s. It is concluded that 1,1'-bi-2-naphthol is the inter-mediate during the synthesis process from 2-naphthol to peri-xanthenoxanthene. The absorption spectrum and photoluminescence spectrum of peri-xanthenoxanthene are symmetric. The maximum absorption and emission wavelength are 443.6 nm and 445.0 nm respectively. The quantum efficiency is 0.95 in CHCl3 solution, indicating it is a good blue organic electroluminescent materials. The HOMO and LUMO energy levels of peri-xanthenoxanthene are determined by the cyclic voltammetry. The experimental results show that the HOMO and LUMO energy levels are 5.45 eV and 3.00 eV that means a good hole transfer ability. The product begins sublime at 238℃, however, it is stable in the air according to the thermogravimetric analysis. The differential scanning calorimetry (DSC) measurement shows that its glass transition temperature is 133℃. By considering the use of peri-xanthenoxanthene as hole transfer layer in OLED, the lifetime of these diodes would be very short since the planar molecular configuration cannot form stable amor-phous membrane.关键词：peri-xanthenoxanthene;microwave carbon bath;2-naphthol113|88|0更新时间：2020-08-11
- 摘要：CN-PPV is one of the important series of PPV and its derivatives, demonstrating very high quantum efficiency of over 4% in a two-layers device, ITO/PPV/CN-PPV/Al. It is widely known that the defects in the polymer backbone can affect the properties of the device. The main structural defects in PPV-type conjugated polymers involve the "tetrahedral" structural segments and the E-double bone configurations. In order to achieve a better understanding to the structure of MEH-CN-PPV, the model compound (8a) (Z,Z-configuration) was synthesized. The Z/E-isomerization of the vinylene moiety with cyano group happened easily under the influence of visible and UV light. (8a) dissolved in chloroform was irradiated in daylight for 2 days under purging nitrogen. Its NMR spectrum become more complex, which showed the occurrence of the Z/E-isomerization. Through a careful separation for this mixture by column chromatography (silica gel, cyclohexane/ dichloromethane 2:5) in the dark, two new compounds (8b) (a green solid) and (8c) (yellow oil) were obtained. According to the 1H-NMR spectra, the configuration of (8b) was E,E and that of (8c) was Z,E. In the 1H-NMR spectrum of the copolymer MEH-CN-PPV, the main signals were similar to (8a), which indicated that the configuration of the copolymer MEH-CN-PPV was mainly Z. Some feeble signals at 6.47×10-6 and 3.32 ×10-6 were similar to the signals of the protons on the vinylene bond and OCH related with the E-configuration in (8b) and (8c). Hence these signals can prove the presence of the E-configuration in MEH-CN-PPV backbone. The ratio between the signal (d) and the signal (a) was 0.09. The contents of the Z/E-configuration could be estimated: for Z-configration was 85% and 15% for E-configration.关键词：MEH-CN-PPV;Z/E-configuration;nuclear magnetic resonance131|301|0更新时间：2020-08-11
- 摘要：Because its unique structure, the rare earth ion has the better fluorescence specific, and could react with many organic ligands to form the good fluorescence complexes. This article simply has introduced syn-thesis of bis β-ketone and studied fluorescence performance of Eu3+ ,Tb3+-bis β-ketone system. This system has the good fluorescence characteristic through its fluorescence spectrum determination and contrast, analysis of the different factor, including the solvent, ligand structure, the influence of pH value on the fluorescence intensity. The experiment result showed: in the system of rare earth(Eu3+ or Tb3+)bis-β-ketone, the luminescence intensity was higher in the ethanol than that in the water. Emulsifier OP enhanced the luminescence greatly.The effect of pH was investigated in the range of 410, but the luminescence signal was observed to be the strongest at pH=6. The effect of different ligands was studied also, and the sequence of the enhance is: H2L1 >H2L2 > H2L3. The Eu3+ has a nice match with the bis-β-ketone ligands, but Tb3+ didn't match with the bis-β-ketone ligands perfectly, and the luminescence intensity of the Eu3+-H2L1 complex is the strongest in three ligands complexes.关键词：Eu3+;Tb3+;bis-β-ketone;rare earth complexes;luminescence116|114|2更新时间：2020-08-11
- 摘要：In biomedicine research field, the fluorescent phenomena of biological sample is feeble and its time relaxation mostly is between fs and ns.By means of ultrashort pulses laser, feeble fluorescence of the biological sample can be detected expediently and efficiently. The object of this study was to explore the ultrafast photodynamic process of hematoporphyrin derivative (HPD) which is a kind of photosensitisers for diagnosing and therapying cancer. By means of ultrafast pulses laser spectral technique and picosecond time-correlated single-photon counting system, fluorescence spectrum,the characteristic of fluorescence lifetime and fluorescence peak intensity fluctuation dependent on time of cancer cells sample and normal cells sample were measured.It was observed that cancer cells sample had special spectral peak at near 645 nm. Moreover, fluorescence lifetime's fast part of cancer cells and normal cells were about 150 and 300 ps respectively, and fluorescence intensity of cancer cells and normal cells decayed approximate 10% and 55% separately in twelve hours. According to the measured fluorescence spectrum curve and analyzed time-resolved fluorescence decay curve, it was calculated that the HPD concentration in cancer cells sample increased two orders of magnitude while the HPD concentration in normal cells sample had no apparent change. What's more, it was computed that the fluorescence lifetimes of cancer cells and normal cells were about 824 and 1 798 ps and that HPD's stay time in cancer cells sample and normal cells sample were about 17 days and 6 days respectively. The results indicated that the differences between cancer cells and normal cells in fluorescence spectrum, the characteristic of fluorescence lifetime and the fluorescence peak intensity dependent on time were large. This study demonstrated that it was feasible to diagnose and therapy cancer using fluorescence spectrum technique. The study also provides an important guidance for further studying and developing the technique of diagnosing and therapying early cancer using ultrashort pulses laser technique and is significant to clinic application.122|97|0更新时间：2020-08-11
- 摘要：Silicon is a traditional semiconduction material, as we all know, and has a broad use in semiconduction industry. But because of its indirect bandgap and rather low light effiency, silicon had not been treated in application in optoelectronic material making process. In 1990, Canham published that porous silicon sample fabricated by electrochemical anodization etch possesses has very intense photoluminescence(PL)emission, and its light efficiency can campare to direct bandgap material GaAs. This report gave a new means to realize Si-based emitting material of photoelectricity integration.The investigation on photoluminescence properties of porous silicon samples made through conventional electrochemical anodization method under different conditions was reported. Two different ways have been used to treat porous silicon samples, including cathodic reduction process and acid treatment. Moreover, we mainly focus on contrast of photoluminescence properties of treated porous silicon samples by two different ways, comparing and analyzing the photoluminescence spectra of different samples. Experimental results indicate that through nitric acid treatment, an increase in luminous intensity of porous silicon can been seen, and the effect is related to nitric acid concentration. The photoluminescence will be enhanced with the nitric acid concentration increasing. Compared with other acids, nitric acid treatment can effectively increase the luminescence intensity of porous silicon and make the luminescence stability of porous silicon better. The results also prove that the process of cathodic reduction can obviously improve luminescence stability of porous silicon and luminescence intensity as well. In this experiment, we found that aging time play a comparative important role in final experimental result. The results showed that the two methods can effectively enhance luminescence efficiency and stability. Moreover, we firstly processed cathodic reduction, then nitric acid treatment, giving a comparsion between the effect of these two methods. A conclusion can be drawn that the method of firstly processed porous silicon samples with nitric acid treatment and secondly cathodic reduction treatment has better effect to porous silicon luminescence intensity and stability than that of firstly cathodic reduction treatment and secondly nitric acid treatment. In addition, we further discussed the possible luminescence model of porous silicon.关键词：porous silicon;cathodic reduction;acid treatment107|87|1更新时间：2020-08-11
- 摘要：Carbon nanotubes field emission display (CNTs-FED) has been regarded as the most promising flat panel display due to its high definition, low power consumption, high brightness, fast response time, wide work temperature range and low cost. As the key material, the properties of CNTs will affect FED characters directly. CNTs with good field emission properties were needed for the FED. The CNTs were synthesized by chemical vapour deposition (CVD) in the temperature range of 500℃~750℃. The morphologies of CNTs depending on growth temperatures were characterized by scanning electron microscope. The as-grown CNTs were mixed with conductive pastes, then screen-printed on the glass substrate coated with a silver conducting layer to form a FED cathode. The dependence of FED properties on the CNTs growth temperatures was studied by using current-voltage (I-V) and luminescence image measurements. The SEM images shew that with the temperature increasing from 500℃ to 700℃, the average diameter of CNTs decreased. By the I-V and luminescence image measurements, it was found that the higher growth temperature, the better FED properties, i.e. lower turn-on emission field,higher emission current and more uniform emission.The field emission experiment of the CNTs cathodes indicated that there is an optimal temperature range (600~700℃) for CNTs growth and being used as field emission cathode. With good pro-perties,bright and stable anode image was observed in diode mode field emission. These results suggested that CVD grown CNTs could be used for cathode fabrication of large area field emission display.关键词：carbon nanotubes(CNTs);field emission display(FED);screen-printing;growth temperature112|222|1更新时间：2020-08-11
- 摘要：Two basic types of methods are presently available to prepare CNTs field emission cathode. The first one is screen printing method by using CNTs paste. The large screen cathode can be made, but it is dif-ficult to control the uniform distribution of CNTs for such method. The CVD method is the second one that is ideally suited to grow film of nanotubes on pre-coating substrates with a metallic catalyst layer, which has been reported by many authors. Although a few of studies on the field emission properties of patterned aligned multi-wall nanotubes (MWNTs) were reported, the catalyst films were patterned by conventional photolithography and etching techniques. This method is too troublesome in application. We reported the CNTs films were directly synthesized on stainless steel substrates by MWPCVD without pre-coating of catalyst layer, and especially investigated the influence of deposition conditions on field emission from such deposited carbon nanotubes films. The source gas for growing the CNTs was a mixture of H2 and CH4. The gas flow rate of H2 is 100 sccm, and the growth pressure was 6.7×103 Pa, deposition time was 10 min. Scanning electron microscopy (SEM) was used to determine the morphology of carbon nanotubes. Raman spectroscopy and XRD were used to analyze the structure of carbon nanotubes. The field emission characteristics of the samples were measured by using a diode structure. The transparent anode was made of coating phosphor onto an ITO coated glass plate. The CNT samples as the cathode were separated from the anode by a china sheet with a suitable hole as the emission area. The gap between the anode and the cathode was 500 μm. The measurement was carried out in vacuum chamber under pressure of 6.5×10-5 Pa. By varying deposition conditions such as gas flow rate, reactive temperature, the optimum conditions for field electron emission of CNTs were found. When gas flow rate of CH4 was 8 sccm, and reactive temperature was 700800℃, the field emission properties of CNTs are the best. At this condition, all CNTs are disorder growth, but are of uniform with the highest density as characterized by SEM. Turn-on field of CNTs is 0.8 V/μm, and emission sites are dense and uniform.关键词：carbon nanotubes (CNTs);MPCVD;field electron emission;Raman spectrum118|218|0更新时间：2020-08-11
- 摘要：Ultraviolet (UV) electroluminescence (EL) from organic light-emitting diode (OLED) with the emitter consisting of Ce3+-complex, Ce-dicyclohexano-18-crown-6(Ce-DC18C6), as dopant, and a hole-transporting layer, 4,4'-bis(9-carbazolyl) biphenyl (CBP) as the host have been investigated. The Ce3+-complex was prepared by reacting cerium chloride with dicyclohexano-18-crown-6 in a methanol. The EL devices with the structure of indium tin oxide (ITO)/copperphthalocyanine (CuPc)/Ce-DC18C6:CBP/2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(Bu-PBD)/LiF/Al were employed to study the UV EL emission properties of the Ce3+ ion, and UV EL radiation peaked at about 376 nm from the Ce3+ ion was firstly observed. Comparing the EL with photoluminescent (PL) excitation and emission spectra, it is speculated that the UV EL emission was proved to be resulted from the 5d-4f transition of the Ce3+ ion in the Ce3+-complex. And we have also found that the UV radiation with shorter wavelength is more valuable for using as excitation source of organic or inorganic phosphors, which will be expected to become solid state illumination with panel feature. A maximum radiance power of our UV-diodes is 13 μW/cm2 for 3%(mass fraction) Ce3+-complex doped CBP device.关键词：ultraviolet-OLED;Ce3+-complex;5d-4f transition;UV radiation source137|81|0更新时间：2020-08-11
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